Today's Message Index:
----------------------
1. 07:37 AM - Nav antenna - The Answer (davidjoyce@doctors.org.uk)
2. 07:53 AM - Re: Nav antenna - The Answer (Alan Burrill)
3. 11:37 AM - Re: Nav antenna (Paul McAllister)
4. 12:48 PM - Re: Algae in Fuel Tank (Nigel Graham)
5. 01:12 PM - ELT (William Daniell)
6. 01:17 PM - Re: Re: Algae in Fuel Tank (Tim Ward)
Message 1
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| Subject: | Nav antenna - The Answer |
Just in case anyone else gets confused by this question, I discover that
both my Comant nav antenna and a brand new certified one have a
resistance from core to sheath (or indeed measured simply between the
two metal limbs of the antenna) of just 0.4 ohms, quite distinct from
Com antennae which have very high resistance. It had struck me that a
short in the connectors or the coaxial cabling might be what is
troubling the nav bit of my GNC255 but it is not so - clearly the two
sections of the nav dipole are connected by some low resistance
structure.
Regards, David Joyce, GXSDJ
On 2017-10-22 18:39, Alan Burrill wrote:
> The are horizontal dipoles and should effectively be open circuit.
>
> Alan
>
> Sent from my iPad
>
> On 22 Oct 2017, at 18:01, davidjoyce@doctors.org.uk wrote:
>
>> Does anyone have a nav antenna (of VOR/Glide slope/Loc variety) conveniently
to hand so that they could measure the resistance across the pin to sheath, or
maybe is clever enough to know what it should be? Am pursuing a glitch and find
that my nav antenna has a very low resistance unlike Com & Transistor antennae.
>>
>> Regards, David Joyce, GXSDJ
Message 2
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| Subject: | Re: Nav antenna - The Answer |
Interesting. The only antennae I have come across with low dc resistance is a
n end fed dipole or a folded dipole where for balancing the impedance a coil
is used.
Looking at the picture in Mendelssohn catalogue for the Corment VOR Antenna I
would not have expected any balancing coils to be used.
Live and learn, sorry if I misled you.
Alan
Sent from my iPad
> On 23 Oct 2017, at 15:35, davidjoyce@doctors.org.uk wrote:
>
> Just in case anyone else gets confused by this question, I discover that b
oth my Comant nav antenna and a brand new certified one have a resistance fr
om core to sheath (or indeed measured simply between the two metal limbs of t
he antenna) of just 0.4 ohms, quite distinct from Com antennae which have ve
ry high resistance. It had struck me that a short in the connectors or the c
oaxial cabling might be what is troubling the nav bit of my GNC255 but it is
not so - clearly the two sections of the nav dipole are connected by some l
ow resistance structure.
>
> Regards, David Joyce, GXSDJ
>
>
>
>
>> On 2017-10-22 18:39, Alan Burrill wrote:
>>
>> The are horizontal dipoles and should effectively be open circuit.
>>
>> Alan
>>
>> Sent from my iPad
>>
>>> On 22 Oct 2017, at 18:01, davidjoyce@doctors.org.uk wrote:
>>>
>>> Does anyone have a nav antenna (of VOR/Glide slope/Loc variety) convenie
ntly to hand so that they could measure the resistance across the pin to she
ath, or maybe is clever enough to know what it should be? Am pursuing a gli
tch and find that my nav antenna has a very low resistance unlike Com & Tran
sistor antennae.
>>>
>>> Regards, David Joyce, GXSDJ
>>>
>>>
>>>
>>>
Message 3
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+1... To what Alan said
On Sun, Oct 22, 2017 at 12:39 PM, Alan Burrill <alanb@dpy01.co.uk> wrote:
> The are horizontal dipoles and should effectively be open circuit.
>
> Alan
>
> Sent from my iPad
>
> On 22 Oct 2017, at 18:01, davidjoyce@doctors.org.uk wrote:
>
> Does anyone have a nav antenna (of VOR/Glide slope/Loc variety)
> conveniently to hand so that they could measure the resistance across the
> pin to sheath, or maybe is clever enough to know what it should be? Am
> pursuing a glitch and find that my nav antenna has a very low resistance
> unlike Com & Transistor antennae.
>
> Regards, David Joyce, GXSDJ
>
>
Message 4
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| Subject: | Re: Algae in Fuel Tank |
Hi Tim,
There are two potential problems, both caused by ethanol in the fuel and both exacerbated
by long periods of inactivity.
If you are experiencing a blotchy opaque jelly like substance that sinks to the
bottom of the tank and collects in your filters, this is most likely water contamination
in the fuel that has undergone phase separation - the ethanol combining
with more water than it can bond to, eventually drops out of suspension.
Typical causes are a leaking fuel filler cap letting water in during heavy rain,
or condensation forming in the air space of a half empty tank in an aircraft
that has been left standing for a long period of time during the misty, clammy
or humid winter months.
The second problem really is a bacterial infection. Airborne acetobacter that breed
during the autumnal months in the fruits and berries found in the countryside
can come into contact with the ethanol fuel via the tank breather pipe. These
feed on the alcohol and produce acetic acid as a by-product. This turns the
normally non-conducting fuel into a conducting mild electrolyte. The acetic
acid will then begin an electrolytic reaction between the brass and copper components
in your fuel system and the softer alloy components - which will corrode
ferociously. The most obvious place to check for this is the Bing float bowl.
Our aircraft have the same life cycle as our lawnmowers. They get dragged out in
the springtime, are used on weekends (if the weather is good) and then get dragged
back into the shed/hangar in the autumn and forgotten for another five
months. Problems almost always occur after the planes are left with half full
tanks (big air space) for long electrolytic of time.
Cars, that use the same fuel don't seem to experience the same problems because
they are used throughout the year and fresh fuel is constantly flushing through
their fuel systems.
Since we can no longer get mogas without ethanol, the only way to prevent this
contamination/corrosion is to ensure that the tanks are always left full at the
end of every flight (the least possible air-space in the tank) during the flying
season. At the end of the flying season, the tanks should be flushed, or
run dry, then filled with a few litres of 100LL (that does not contain ethanol)
and the engine run to draw this through the whole system. The aircraft can then
be laid up.
I have pictures that illustrate of both problems - but can't post them up at the
moment as I am away from home.
Hope this helps
Nigel
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=473815#473815
Message 5
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Does anyone have a firm recommendation for an ELT that is light and has its
own GPS?
Many thanks
Will
Message 6
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| Subject: | Re: Algae in Fuel Tank |
Many thanks Nigel. It seems to have decreased lately after checking the filters.
Will monitor the situation closely.
Cheers,
Tim
Tim Ward
12 Waiwetu Street,
Fendalton,
Christchurch, 8052
New Zealand
ward.t@xtra.co.nz
Mob +64 210640221
> On 23/10/2017, at 12:48 PM, Nigel Graham <nigel_graham@m-tecque.co.uk> wrote:
>
>
> Hi Tim,
>
> There are two potential problems, both caused by ethanol in the fuel and both
exacerbated by long periods of inactivity.
>
> If you are experiencing a blotchy opaque jelly like substance that sinks to the
bottom of the tank and collects in your filters, this is most likely water
contamination in the fuel that has undergone phase separation - the ethanol combining
with more water than it can bond to, eventually drops out of suspension.
>
> Typical causes are a leaking fuel filler cap letting water in during heavy rain,
or condensation forming in the air space of a half empty tank in an aircraft
that has been left standing for a long period of time during the misty, clammy
or humid winter months.
>
> The second problem really is a bacterial infection. Airborne acetobacter that
breed during the autumnal months in the fruits and berries found in the countryside
can come into contact with the ethanol fuel via the tank breather pipe.
These feed on the alcohol and produce acetic acid as a by-product. This turns
the normally non-conducting fuel into a conducting mild electrolyte. The acetic
acid will then begin an electrolytic reaction between the brass and copper
components in your fuel system and the softer alloy components - which will corrode
ferociously. The most obvious place to check for this is the Bing float
bowl.
>
> Our aircraft have the same life cycle as our lawnmowers. They get dragged out
in the springtime, are used on weekends (if the weather is good) and then get
dragged back into the shed/hangar in the autumn and forgotten for another five
months. Problems almost always occur after the planes are left with half full
tanks (big air space) for long electrolytic of time.
>
> Cars, that use the same fuel don't seem to experience the same problems because
they are used throughout the year and fresh fuel is constantly flushing through
their fuel systems.
>
> Since we can no longer get mogas without ethanol, the only way to prevent this
contamination/corrosion is to ensure that the tanks are always left full at
the end of every flight (the least possible air-space in the tank) during the
flying season. At the end of the flying season, the tanks should be flushed, or
run dry, then filled with a few litres of 100LL (that does not contain ethanol)
and the engine run to draw this through the whole system. The aircraft can
then be laid up.
>
> I have pictures that illustrate of both problems - but can't post them up at
the moment as I am away from home.
> Hope this helps
> Nigel
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=473815#473815
>
>
>
>
>
>
>
>
>
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